Person.prototype.say = function () {
  console.log('我是周圣');
}
function Person() {
  this.name = '周圣'
}
Boy.prototype = new Person()  // {name: '周圣'}.__proto__ === Person.prototype.__proto__ === Object.prototype.__proto__ == null
function Boy() {
  this.age = 18
}
let b = new Boy()  // {age: 18}.__proto__ === Boy.prototype
console.log(b.run);